Brief Description of the Prior Art
Heretofore, many through-conduit gate valve assemblies with expanding gates have comprised a gate having a female V-surface formed in the upstream side of the gate and having a floating segment mounted on the gate, and carrying a complementary male V-surface which engages and coacts with the female V-surface on the gate. The described gate assembly is positioned adjacent seating surfaces within the valve body, and the gate assembly generally moves in a direction perpendicular to the conduit axis (direction of fluid flow through the valve) and parallel to the seating faces. Sealing during opening and closure is effected by the segment being wedged outwardly from the gate in a direction perpendicular to the axis of the stem to effect sealing engagement with the seat faces. Such expanding gate valves may have the gate formed integrally with the stem, or the gate may be connected to the stem with a floating connection, or the gate may be threadedly connected to the stem.
In expanding gate valves of the type described, movement of the gate in a direction normal to the conduit axis brings the floating segment into contact with a stop or other interfering structure which arrests further movement of the segment with the gate in a direction normal to the conduit axis. This causes the segment to be wedged outwardly in a movement of gate expansion, so that the segment is brought into sealing contact with the valve seat. Such expansion of the segment along the conduit axis and substantially perpendicular to the stem axis results from the wedging action of the cooperating V-surfaces carried on the segment and on the gate.
The wedging action causing expanding movement of the segment occurs in the fully closed or the fully opened position of the valve, and, as indicated, results from predetermined, selectively located fixed stops, such as parts of the valve body, which are interposed in the path of movement of the segment as it moves with the gate. These stops arrest further movement of the segment in a direction parallel to the axis of the gate stem. When the gate is moving between the open and the closed positions, the segment is caused to collapse upon, or nest with, the gate as a result of the complementary interfitting of the engaged V-surfaces.
In order for the valve to be smoothly and easily operable, and to avoid damage to the valve stem or gate, it is essential that the wedging action of the gate segments occur in only the open and/or closed positions, and that the segment remain in the collapsed condition when the gate is moving between the open and closed positions within the valve body. This prevents unnecessary dragging or binding of the gate assembly against the valve seat faces at a time when the high integrity sealing is not required. Moreover, any pre-expansion of the segment during travel, also referred to as back-wedging, may result in excessive torque being applied to the stem in order to operate the valve, thereby causing the valve assembly to jam, or even causing twist-off and failure of the stem.
In a gate assembly in which the gate is connected to the stem with a floating connection, for example, with a T-head, both the gate and the segment expand axially along the conduit (fluid flow) axis at the time of closure and opening of the valve. When the gate is of a non-floating type, however, because of a rigid connection between the gate and the stem, only the segment can expand upon closure and opening of the valve. The restraint of the stem prevents the gate from moving in an axial direction.
As a result of such stem restraint, a bending moment is created on the stem in the plane encompassing its axis and the conduit axis (i.e., in the direction of fluid flow). This makes the valve more difficult to operate, and presents the possibility of jamming the valve assembly. When the load on the gate and stem is relieved, the fluid pressure in the conduit, acting on the segment and aided by centralizing levers and/or torsion springs, often employed in expanding gate valves of the type described, forces the segment to nest or collapse into the gate, thus relieving the pressure on the seat faces. The gate assembly can then travel between the position of opening and closing without dragging or binding due to unnecessary contact with the seat faces.
If the fluid pressure in the conduit on the downstream side of the gate assembly (the side opposite the side of the gate which carries the wedge), should build and act with excessive back pressure on the gate, the nesting or collapsing ability of the gate assembly becomes impaired, thereby causing problems as a result of back-wedging or pre-expansion of the segment. The valve consequently becomes very difficult to operate, and in extreme cases, cannot be operated at all.
For the described reasons, the expanding gate valve assembly having a single V-surface on one side of the gate for the accommodation of the V-shaped male protuberance on the wedge is a unidirectional assembly, and can be mounted in the valve body for operation in only one direction of fluid flow. In other words, the wedge must be located on the upstream or high pressure side of the valve gate in order for the gate assembly to function.
In most prior art expanding gate valve assemblies, the V-surfaces formed in the gate, and projecting from the wedge, have generally consisted of two intersecting inclined surfaces forming a single "V", and the "V" has been formed to a location relatively deep in the gate in order that there is adequate contact surface between the intersecting V-surface on the wedge, and the intersecting V-surface on the gate. Such adequate contact surface provides some stability to the wedge as it moves to its sealing position. The necessity for this relatively large surface area of contact between the wedge and the gate at the interacting V-surfaces has made it necessary to make the gate relatively thick in a transverse sense. Such greater gate thickness, of necessity, causes the valve body chamber to be larger, thus resulting in a larger overall valve assembly. This, in turn, results in increased manufacturing cost for the valve.
Expanding gate valves of the type described, having a gate with a movable segment mounted thereon are shown in U.S. Pat. No. 4,189,127; U.S. Pat. No. 4,531,710; U.S. Pat. No. 4,179,009; U.S. Pat. No. 4,188,014; U.S. Pat. No. 4,188,016; U.S. Pat. No. 4,279,404; U.S. Pat. No. 4,341,369; U.S. Pat. No. 4,334,666; U.S. Pat. No. 3,823,911 and U.S. Pat. No. 4,530,488.
In substantially all expanding gate valves as they are presently constructed, the angle .alpha. which is included between the V-surface and the axis of the stem (the direction of opening and closing movement of the valve gate) is generally of a magnitude of between about 10.degree. and about 18.degree.. As the magnitude of the angle .alpha. is decreased, the ease with which the segment can collapse into the gate following opening and closing is reduced, but a lower operating torque is required to open and close the valve. Conversely, the larger the angle .alpha., the more readily and easily the wedge will collapse into the gate following opening and closing of the valve, but a higher operating torque is required in order to open and close the valve. Moreover, the thickness of the valve must be increased in order to accommodate the single V-notch cut to a deeper location within the gate to afford adequate surface area of contact between the wedge and the gate to stabilize and evenly support the wedge in its expanding movement.
A gate valve is disclosed in Trowe U.S. Pat. No. 1,521,531, and this valve includes two axially movable wedge-shaped segments or valve discs which are caused to move outwardly by a threaded shaft which, when turned, causes an upward movement of a wedge nut. This wedge nut can only be accommodated in its upward movement by an upwardly yielding movement of a wedge member. In other words, the wedge nut, as it moves upwardly, carries with it a wedge member. The wedge nut forces this wedge member upwardly along the axis of the threaded shaft, and as the wedge member moves upwardly, the two opposed valve discs are forced outwardly away from the gate.
The only inclined wedging-camming leg or surface present in the structure of the Trowe valve is the interface of each of the valve discs, each of which, the patentee states, is at a slight inclination to the outer face. It is these inclined faces, however, upon which the wedge member acts during the operation of the valve. The threaded shaft is not touched by the inner inclined interface of either valve disc at any time during operation of the valve. In the Trowe structure, there is actually no gate which corresponds to the gate of this present invention, as such gate coacts with movable segments which are moved out against seats. Rather, there is only the threaded shaft which causes the up-and-down movement of the wedge nut which moves upwardly and downwardly along the axis of the threaded shaft. This action by the wedge nut in turn forces the valve discs outwardly into sealing contact with valve seats disposed on opposite sides of the cavity centrally located in the valve body. While it appears that the valve discs are screwed downwardly as the nut and wedge member are moved upwardly, this downward movement of the valve discs on the threaded stem or gate has nothing to do with the concurrent outward movement of the valve discs. This is caused by, and results solely from, the upward movement of the wedge member.
The handle, stem and other operator devices used in the Trowe patent gate valve are also complicated. A first linkage must be initially manually actuated up or down in order to physically displace, by reciprocation, the entire stem, the threaded shaft, the wedge nut, wedges and valve discs. Once they have been moved up or down into a position where this entire assemblange of multiple elements closes the fluid flow passageway across the valve in a gross or general sense, sealing is then next effected by rotation of an elongated valve stem shaft which passes through a collar carried by the manually actuated linkage previously used. There are thus two operators provided in the Trowe valve with these operators being manually manipulated at two different times during the opening, closing and sealing of the valve.
The gate valve shown in Ladd U.S. Pat. No. 880,674 also has a sequentially manipulated compound operator system. A manually operated linkage is first used to move the entire stem up or down, and with it, the multiple part valve mechanism. After this, the elongated valve stem is rotated about its longitudinal axis to set the valve into a sealing mode. Two discs are located on opposite sides of the threaded shaft or rotatable stem, which is itself reciprocated within the valve body. The patentee refers to these discs as "gates". These "gates" are caused to move in a divergent fashion concurrently with the convergence toward each other of a pair of spreading blocks. As these spreading blocks are moved toward each other by the interaction of the two blocks with oppositely pitched threads formed on the rotatable stem, the two wedge blocks, or spreading blocks, force the so-called gates away from each other on opposite sides of the valve cavity. They are ultimately forced into sealing contact with the seats as a result of the movement of the wedge or spreading blocks toward each other.
As the spreading blocks move toward each other, the inclined planes formed by one frustoconical surface on each spreading block forces a gate segment out into sealing contact with a corresponding seat in the valve body. When the stem is rotated in the opposite direction, the spreading or wedging blocks are moved away from each other. This releases the gates which then unseat and allow the entire stem to be reciprocated upwardly within the valve by means of the extra handle or operator first mentioned above. This upward movement continues until two gates and the cooperating spreading blocks are moved upwardly into the bonnet of the valve, and thus clear the fluid flow passageway through the valve. There are thus no segments in the Ladd valve which are forced by moving, inclined, spaced, wedging-camming legs or surfaces carried on the gate or the stem itself so as to move into sealing contact with seats in the valve body.
In U.S. Pat. No. 4,405,113 to Erwin, a reciprocating expandable gate valve is disclosed. This gate valve has a first main stem which moves the entire multiple part gate as a unit in reciprocation upwardly and downwardly with respect to the fluid flow passageway, or stated differently, transversely across the valve body.
The main stem further has coaxially aligned therewith, a cam drive shaft having first and second oppositely threaded sections which function to respectively engage the main stem and a central gate block. The central gate block carries a plurality of cam surfaces thereon. These cam surfaces are contiguous to each other, and they cooperate with seal blocks which also carry cooperating contiguous cam surfaces which interfit with the cam surfaces on the gate block. The seal blocks are moved outwardly as a result of movement of the central gate block, and the coaxial cam drive shaft is moved by rotation of this shaft after the entire valve assembly has been placed across the fluid flow passageway. The cam surfaces formed on the gate block consist of a plurality of contiguous saw-tooth indentations or triangular steps in the gate block which cooperate with complementary cam surfaces on the seal blocks. The complicated compound or dual stem structure disclosed in this patent is the mechanism by which the upper central gate block is caused to undergo a reciprocating up-and-down movement within a certain limited range previously established by rotation of the main stem to set the gate into position within the valve body.
The canted planar camming surfaces which are carried on the central gate block of the Erwin patent are arranged in a saw tooth array. Each camming surface is immediately contiguous to an adjacent camming surface, and each is defined as a triangular protuberance which includes an acute angle. There are no spaced wedging-camming surfaces having a substantial intervening surface therebetween, and placing the wedging-camming surfaces at a significant distance from each other. Moreover, there is no obtuse angulation, but there is rather an acute angle, formed between any of the contiguous wedging-camming surfaces carried on the gate block.
There are a pair of well spaced, wedging-camming surfaces carried on the gate and segment in the present invention. Therefore, balancing and two point support of the segments, which are in contact with the spaced wedging-camming surfaces at all times during expansion of the segments, assures that such segments will always seat squarely against the seat after they have been wedged outwardly by the wedging camming surfaces with which they are in contact. In other terms, the segments do not rock or cant during their sealing movement, but rather move smoothly and evenly against the seat.
The spacing of the two parallel wedging-camming surfaces or legs in the present invention is by a distance which is at least ten percent of the distance across the fluid flow passageway through the valve, and which is to be sealed, and such spacing distance is preferably at least a major portion of the distance across such fluid flow passageway. In most applications of the invention, the distance across the fluid flow passageway can also be equated to the inside diametric distance across the annular seating surface positioned within the valve body adjacent the central cavity in the valve body and extending around the fluid flow passageway. Described in yet another way, the wedging-camming surfaces on the gate are spaced from each other by a distance such that, at the time the segment is undergoing expansion, it is moved away from the gate so that its sealing face remains oriented in the same angular attitude relative to the seating surface within the valve body against which it is to seal. This orientation, which remains constant, is usually parallel to that seating surface while the segment is being cammed toward it. This assures that there is uniform sealing pressure on the seating surface by the sealing face of the segment when sealing is effected, and the described spacing of the wedging-camming surfaces assures that the necessary stability is realized to accomplish this.
In contrast, in the Erwin patent, there are a series of contiguous, saw tooth-shaped camming elements, with only an acute angle defined at the intersection of each of these camming surfaces. The outer seal blocks, provided as a part of one embodiment of the valve illustrated in the Erwin patent, will frequently ride upon, and bear primarily on, only one or at most two of these triangular camming surfaces. This is because this camming surface is the highest, and projects out further than the others. This relationship will frequently occur simply due to the difficulty of machining precisely identical mating saw-tooth surfaces (of the type shown in the Erwin patent) over all of the gate, and cooperating equally with all the seal block camming surfaces. The seal blocks consequently will frequently ride on, and bear primarily upon, only a single one of the camming surfaces which is higher (that is, projects out further) than the others. It is simply not possible, because of manufacturing tolerances, to predict or reckon which of the triangular wedge teeth will protrude out slightly further than the others. Thus, there will be an unpredictable rocking movement of the gate in relation to the seal block due to this very localized support. By contrast, where there are only two of the well spaced wedging-camming surfaces--spaced transverse to the fluid flow axis--as is true of the invention here under consideration, the two spaced wedging-camming surfaces carried on the gate will always be in mating and supporting contact with two wedging-camming surfaces carried on the segment. Any slight shifting of the segment which is required during sealing will still be accommodated by the two, spaced, parallel wedging-camming surfaces as these are formed on the gate. This allows the segment sealing face to be truly self-aligning with the seat, even where the seat is canted or cocked, either by design or due to manufacturing tolerances, or as a result of extended usage.
Danish Patent 50,251 discloses a gate valve in which the gate remains in one position relative to the fluid flow passageway through the valve body at all times during the operation of the valve. Two segments are carried on the gate and these are threaded downwardly by rotation of the gate until the lower ends of these segments strike a pair of inclined surfaces provided on a pair of wedge elements. These wedge elements are secured to the inner side of the valve body, so that once the segments are screwed down at this location, the lower ends of the segments are deflected outwardly by the wedging action of these inclined surfaces. This outward wedging continues until the segments come to bear against the seats located within the valve body on opposite sides of the central valve cavity.
This action is not caused by any structure carried on the gate, but results instead from the segments being canted or cocked sideways as they come in contact with fixed, or non-moving wedge elements projecting inwardly into the valve cavity from the valve body. Further rotation of the helically threaded gate will ultimately cause the tops of these two segments to also be forced out into contact with the seating surfaces at that location within the valve body. The sealing force applied to the two segments is not even or uniform, and the segments do not move so that their sealing surfaces remain parallel to the seating surfaces carried within the valve body. Neither do they seat with the same force at the same time.
The valve shown in the Danish patent causes inordinately high loading on one, or at most two, threads of the threaded cylindrical gate. Due to the pivoting of the segments at their lower end at the time they encounter the inclined surface on the wedge lugs, the lowest thread on the gate will carry a predominance of the load at that time, thereby causing premature failure of the gate thread at this location.